Screen goes blank

Sometimes my screen goes completely blank, then comes back on, and the computer seems ok, then I realize that it actually crashed, and I have a lot problems trying to shut down.
What could be causing this ? Thank's.

 

It could be some thermal intermittent hardware issue. Clean out the dust and check the fans.

 

Dust and fans are ok, but, I found the following errors reported in
System Information for the last time the crash occurred:

2 Dhcp errors

"The IP address lease 66.69.131.3 for the network card...has been denied. "

"Your computer has lost the lease to its address 192.168.100.2 on the network card. "

The computer was in a network at one time, but not currently in a network.
Could I disable, or delete the networking configuration to solve this problem ?

Thank's

 

Certainly.

start => run => cmd and OK. Then at the > prompt

Code:

Netsh int ip reset C:\iplog.txt

and ENTER.